why braces were automatically added to equation after I reopen Lyx file

[Asm warrior]

I have equation like below:
\begin{equation}
^{C}v_{B}=^{C}(^{U}V_{B})\end{equation}

but when I save the lyx file, then reopen it, it became

\begin{equation}
^{C}v_{B}={}^{C}(^{U}V_{B})\end{equation}

You can see the screen shot before and after the lyx was reopened.

So, the automatically added brace(there will be a rectangle before the 
superscript)was really ugly shown in Lyx editor, is it possible to 
disable this functionality. I just don't want these change.

Thanks.

<<attachment: reopen.png>><<attachment: before.png>>